Rapid curing thiol epoxy resin with improved compression strength performance

ABSTRACT

Aspects described herein generally describe epoxy resins and methods of epoxy resin formation. In some embodiments, a resin includes the reaction product of one or more polythiols, one or more polyepoxides, one or more fillers and one or more amine catalysts. Polythiols have between two and about ten thiol moieties. Polyepoxides have between two and about ten epoxy moieties. One or more amine catalysts of the formula NR 1 R 2 R 3 , wherein each of R 1 , R 2 , and R 3  is independently linear or branched C1-20 alkyl or two or more of R 1 , R 2 , and R 3  combine to form cycloalkyl. The resin has a compressive strength of at least 14 ksi at 2% offset at 70° F. and at least 8 ksi at 2% offset at 190° F.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/931,518 filed Nov. 3, 2015. The above-mentioned application is herebyincorporated by reference.

FIELD

Aspects described herein generally relate to epoxy-thiol resins andmethods of curing epoxy-thiol resins.

BACKGROUND

Thermoset plastic/prepreg and liquid shim material are typically used inaerospace vehicle assembly to eliminate gaps and dimensional differencesbetween two joined parts. Liquid shims are commonly epoxy-basedstructural adhesive materials that possess high compressive strengths.For gaps wider than ˜3 millimeters, solid shims made out of thermosetplastic or prepreg are used, but in cases where gaps are less than ˜3millimeters or for wide area fit up, a flowable cured polymeric resinmaterial (a liquid shim) is employed.

Key properties in a liquid shim material involve pot life, cure time,compressive strength, resistance to cyclic fatigue, and optimal rheologyfor convenient application to vehicle surfaces. Longer pot life allowsthe assembly of larger components and also aides in cleanup of unusedmaterial. Excessively long pot life, however, interferes with productionthroughput, as the shim typically needs time to reach the final curedstate before assembly can continue. A limitation of state of the artliquid shims is the relationship between pot life and cure timeresulting in shims with either impractically short working times orslow, inefficient cure times. Preferably, a liquid shim material willhave a lengthy pot life combined with a rapid cure time for greatestmanufacturing efficiency. In an ideal case, a user activated triggerwould aid the transition between these two regimes. Heat may be used toachieve such an on/off transition. However, manufacturing of commercialaircraft involves strict limits on the degree of heating that can beapplied during assembly processes (typically <140° F.). As a result, thecure transition must be developed to occur in a more narrow range thanmany heat activated systems.

Current state of the art epoxy resins (such as liquid shims) are amineepoxy based resins that meet the basic requirements for use as adhesivesin aerospace vehicles. These resins show typical cure times of 8-9 hrsat ambient temp and 1.5-2 hrs at 140° F. while possessing a compressivestrength of ≥8 ksi@2% offset at 190° F. Manufacturing flexibility withsuch compositions is limited due to the relationship between pot lifeand cure time. Accelerated cure times typically result in short,impractical pot lives while lengthy pot life compositions slowmanufacturing efficiency. Furthermore, attempts at epoxy-thiol basedresins thus far do not provide resins with adequate mechanical integrity(i.e., compressive strength) to achieve the performance of the currentstate of the art systems and meet modern aerospace materials standards.

Therefore, there is a need in the art for methods for forming resins andresins with adequate pot life, controllable curing times to form aresin, and mechanical properties that meet aerospace materialsstandards.

SUMMARY

Aspects described herein generally relate to epoxy resins and methods ofcuring epoxy resins.

In some examples, a resin includes the reaction product of one or morepolythiols, one or more polyepoxides, one or more solid particulatefillers, and one or more amine catalysts. The one or more polythiols mayhave between two and about ten thiol moieties. The one or morepolyepoxides have between two and about ten epoxy moieties. The one ormore amine catalysts of the formula NR₁R₂R₃, wherein each of R₁, R₂, andR₃ is independently linear or branched C1-20 alkyl or two or more of R₁,R₂, and R₃ combine to form cycloalkyl. The resin has a compressivestrength of at least 14 ksi at 2% offset at 70° F. and at least 8 ksi at2% offset at 190° F.

In some examples, a vehicle component has a cured epoxy-thiol resindisposed thereon. The epoxy-thiol resin has a compressive strength of atleast 14 ksi at 2% offset at 70° F. and at least 8 ksi at 2% offset at190° F.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toaspects, some of which are illustrated in the appended drawings. It isto be noted, however, that the appended drawings illustrate only typicalaspects of this present disclosure and are therefore not to beconsidered limiting of its scope, for the present disclosure may admitto other equally effective aspects.

FIG. 1 illustrates glass transition of epoxy-thiol resins, according toan aspect of the disclosure.

FIG. 2 illustrates compressive strength at room temperature of 92.5%epoxy-thiol resin and EA9377 epoxy-amine, according to an aspect of thedisclosure.

FIG. 3 illustrates compressive strength at elevated temperature of 92.5%epoxy-thiol resin and EA9377 epoxy-amine, according to an aspect of thedisclosure.

FIG. 4 illustrates effect of soak time at 220° F. of 92.5% epoxy-thiolresin, according to an aspect of the disclosure.

FIG. 5 illustrates pot life of an epoxy-thiol resin and EA9377epoxy-amine, according to an aspect of the disclosure.

FIG. 6 illustrates cure kinetics at elevated temperature of anepoxy-thiol resin and EA9377 epoxy-amine, according to an aspect of thedisclosure.

FIG. 7 illustrates the effect of increased temperature on pot life andshear modulus, according to an aspect of the disclosure.

FIG. 8a illustrates compressive strength at elevated temperature of anepoxy-thiol resin and EA9377 epoxy-amine, according to an aspect of thedisclosure.

FIG. 8b illustrates compressive strength at room temperature of anepoxy-thiol resin and EA9377 epoxy-amine, according to an aspect of thedisclosure.

FIG. 9 illustrates compressive strength of a 92.5% epoxy-thiol resin andan epoxy-thiol resin, according to an aspect of the disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of one aspectmay be beneficially incorporated in other aspects without furtherrecitation.

DETAILED DESCRIPTION

The descriptions of the various aspects of the present disclosure havebeen presented for purposes of illustration, but are not intended to beexhaustive or limited to the aspects disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the described aspects.The terminology used herein was chosen to best explain the principles ofthe aspects, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the aspects disclosed herein.

Aspects described herein generally describe epoxy resins and methods ofepoxy resin formation. Epoxy-thiol resins described herein meet requiredaerospace material properties. In particular, epoxy-thiol resinsdescribed herein meet or exceed the compressive strength performance ofthe current state of the art epoxy-amine resins while also demonstratinga latent thermally triggered rapid curing behavior.

In some examples, a cured resin includes the reaction product of one ormore polythiols, one or more polyepoxides, one or more solid particulatefillers, and one or more amine catalysts.

In some examples, a vehicle component has a cured epoxy-thiol resindisposed thereon. The epoxy-thiol resin has a compressive strength of atleast 14 ksi at 2% offset at 70° F. and at least 8 ksi at 2% offset at190° F.

In some examples, a resin includes one or more polythiols having betweentwo and about ten thiol moieties. In some examples, at least one of theone or more polythiols is of the formula SH—R—SH. R may be selected fromalkyl, cycloalkyl, thiol-substituted alkyl, and thiol-substitutedcycloalkyl. The one or more polythiols may have an equivalent molecularweight of between about 30 to about 100. In some embodiments, eachinstance of the polythiol is independently 1,2,3-propanetrithiol,1,2,4-tris(2-mercaptoethyl) cyclohexane, and 1,3,5-tris(2-mercaptoethyl)cyclohexane, and the like.

In some examples, the mixture includes one or more polyepoxides havingbetween two and about ten epoxy moieties. Without being bound by theory,an epoxy moiety of the one or more polyepoxides interacts, for exampleas an electrophile, with a thiol moiety, as a nucleophile or hydrogenbond donor, of the one or more polythiols. In some examples, eachinstance of the one or more polyepoxides is independentlyN,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (e.g., Araldite MY721) and/or poly[(phenyl glycidyl ether)-codicyclopentadiene] (e.g.,Tactix 556). In some examples, the molar ratio of polyepoxide topolythiol is between about 0.7 to about 0.99, such as about 0.8 to about1.2, such as about 0.85 to about 0.95. In some examples, the molar ratioof polyepoxide to polythiol is about 0.90. Without being bound bytheory, a subtle change in the molar ratio may affect reactivity andresin network formation, and ultimately affect compressive strength of aresin. In some examples, a desired compressive strength is achieved witha molar excess of polythiol.

In some examples, the mixture may include one or more solid particulatefillers. The identity and amount of one or more solid particulatefillers affects viscosity of a pre-cured resin for workability beforecuring. In some examples, each instance of the solid particulate filleris independently crystalline silica, fumed silica, methylated fumedsilica, alumina, mica, silicates, talc, aluminosilicates, bariumsulfate, diatomite, calcium carbonate, calcium sulfate, carbon,wollastonite, and the like. The one or more solid particulate fillersmay be between about 10% wt to about 75% wt of the resin to yield aresin having a workable viscosity before curing. The one or more solidparticulate fillers may be between about 50% wt to about 55% wt of theresin to yield a resin having a workable viscosity before curing.Crystalline silica may be 1-10 μm crystalline silica. Methylated fumedsilica may be hexamethyldisilazane (HMDZ) modified fumed silica.

In some examples, the mixture includes one or more amine catalysts ofthe formula NR₁R₂R₃, wherein each of R₁, R₂, and R₃ is independentlylinear or branched C1-20 alkyl or two or more of R₁, R₂, and R₃ combineto form cycloalkyl. Without being bound by theory, the one or more aminecatalysts promote deprotonation of thiol moieties of the one or morepolythiols, which promotes nucleophilic attack of the one or morepolythiols with electrophilic epoxy moieties of the one or morepolyepoxides. Without being bound by theory, the greater thedepotonating ability of the one or more amine catalysts and/or thegreater the amount of the one or more amine catalysts in the mixture,the faster resin curing will occur (which will shorten pot life and curetime). The amount and identity of the one or more amine catalysts notonly may affect pot life and cure time, but may also affect compressivestrength of a resin. In some examples, R₁ and R₂ are each a shorteralkyl than an R₃ alkyl. In some examples, each instance of R₁ and R₂ isindependently selected from C1-6 alkyl and R₃ is selected from C7-20alkyl. In some examples, each instance of the one or more aminecatalysts is independently selected from diisopropylethylamine,N-alkyl-piperidine, N-alkyl-piperazine, 1,4-diazabicyclo[2.2.2]octane,1,8-diazabicyclo[5.4.0]undec-7-ene, trimethylamine, triethylamine,tripropylamine, N,N-dimethylethylamine, N,N-dimethylpropylamine,N,N-dimethylbutylamine, N,N-dimethylpentylamine, N,N-dimethylhexylamine,N,N-dimethylheptylamine, N,N-dimethyloctylamine, N,N-dimethylnonylamine,N,N-dimethyldecylamine, N,N-dimethylundecylamine,N,N-dimethyldodecylamine, N,N-dimethyltridecylamine,N,N-dimethyltetradecylamine, N,N-dimethylpentadecylamine,N,N-dimethylhexadecylamine, N,N-dimethylheptadecylamine,N,N-dimethyloctadecylamine, N,N-dimethylnonadecylamine,N,N-dimethyleicosylamine, N,N-diethylpropylamine, N,N-diethylbutylamine,N,N-diethylpentylamine, N,N-diethylhexylamine, N,N-diethylheptylamine,N,N-diethyloctylamine, N,N-diethylnonylamine, N,N-diethyldecylamine,N,N-diethylundecylamine, N,N-diethyldodecylamine,N,N-diethyltridecylamine, N,N-diethyltetradecylamine,N,N-diethylpentadecylamine, N,N-diethylhexadecylamine,N,N-diethylheptadecylamine, N,N-diethyloctadecylamine,N,N-diethylnonadecylamine, N,N-diethyleicosylamine,N,N-dipropylbutylamine, N,N-dipropylpentylamine, N,N-dipropylhexylamine,N,N-dipropylheptylamine, N,N-dipropyloctylamine, N,N-dipropylnonylamine,N,N-dipropyldecylamine, N,N-dipropylundecylamine,N,N-dipropyldodecylamine, N,N-dipropyltridecylamine,N,N-dipropyltetradecylamine, N,N-dipropylpentadecylamine,N,N-dipropylhexadecylamine, N,N-dipropylheptadecylamine,N,N-dipropyloctadecylamine, N,N-dipropylnonadecylamine, andN,N-dipropyleicosylamine.

In some examples, the one or more amine catalysts isN,N-dimethyltetradecylamine. The one or more amine catalysts may be asalt. Without being bound by theory, an amine catalyst that is a saltcures an epoxy-thiol resin more slowly than a neutral form of the aminecatalyst, and may affect pot life, cure time, and/or compressivestrength. The one or more amine catalysts may be between about 0.1% wtto about 10% wt of the resin. The one or more amine catalysts may bebetween about 1% wt to about 3% wt of the resin. The amount of the oneor more amine catalysts may affect pot life, cure time, and/orcompressive strength of a resin.

In some examples, the resin contains an adhesion promoter in order toincrease interfacial adhesion strength between the adhesive and vehiclecomponent. Adhesion promoter includes silane and alkoxy substitutedsilane. Adhesion promoters may be used to promote bonding of a vehiclecomponent to a resin reactive group such as an epoxide, amine, or thiol.

In some examples, the resin has a compressive strength of at least 14ksi at 2% offset at 70° F. and at least 8 ksi at 2% offset at 190° F.,which meets required aerospace material properties.

In some examples, a method of forming a resin includes forming a resincomposition by mixing one or more polythiols of the formula SH—R—SH,where R is alkyl, cycloalkyl, thiol-substituted alkyl, andthiol-substituted cycloalkyl with one or more polyepoxides havingbetween two and about ten epoxy moieties, one or more solid particulatefillers, and one or more amine catalysts of the formula NR₁R₂R₃, whereineach of R₁, R₂, and R₃ is independently linear or branched C1-20 alkylor two or more of R₁, R₂, and R₃ combine to form cycloalkyl. The methodof forming a resin further includes applying the resin composition to avehicle component surface, and curing the resin composition.

In some examples, curing the resin composition is performed at atemperature between about 70° F. and about 140° F. Methods may includeforming the resin composition by mixing one or more polythiols, one ormore polyepoxides, and one or more solid particulate fillers beforeadding the one or more amine catalysts to the mixture, which allowsadditional control of curing of the mixture. For example, curing of amixture may be delayed until a final component, such as the one or moreamine catalysts, one or more polythiols, and/or one or morepolyepoxides, is included in the mixture. A delay in curing may allowfor storage and/or transport of a mixture. Curing a resin may beperformed at about 140° F. to achieve a shear modulus plateau within 30minutes of curing. Curing a resin may be performed at about 70° F.,where the resin composition has a pot life of between about 60 minutesto about 300 minutes, for example about 90 minutes.

As described herein, the term “alkyl” may include, but is not limitedto, a linear or branched acyclic alkyl radical containing from 1 toabout 20 carbon atoms. In some examples, alkyl is a C1-10alkyl,C1-7alkyl or C1-5 alkyl radical. Examples of alkyl include methyl,ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, sec-butyl, andthe like.

As described herein, the term “cycloalkyl” may include, but is notlimited to, a monocyclic, bicyclic or tricyclic cyclized ring system of3 to about 15 carbon atoms that is fully or partially saturated.Examples of cycloalkyl include cyclopentyl, cyclohexyl, cycloheptyl, andthe like.

Many commercially available polythiol precursors possess large averagedistance (on a molecular scale) between thiol groups (i.e., largeequivalent molecular weight per thiol moiety), often having equivalentmolecular weight values of between 300 and 600. A large equivalentmolecular weight of polythiol precursors provides greater flexibility inthe resin network especially at high temperature. The greaterflexibility compromises compressive strength. Polythiols of the presentdisclosure have smaller average distance between thiol groups (ascompared to commercially available polythiol precursors) (i.e., smallequivalent molecular weight per thiol moiety), which improvescompressive strength of epoxy-thiol resins. In some examples, polythiolsof the present disclosure have equivalent molecular weights of betweenabout 5 to about 250, such as about 20 to about 115, such as about 30 toabout 100.

EXAMPLE 1: RESIN 1

As shown in Table 1, Resin 1 contains 3.24 grams of Araldite MY 721,1.08 grams of Tactix 556, 3.13 grams of1,2,4-tris(2-mercaptoethyl)cyclohexane (TMC), 8.08 grams of microsilica, 0.32 grams of hexamethyldisilazane (HMDZ) modified fumed silica,and 0.15 g of N,N-dimethyltetradecylamine (DMTA). Resin 1 has a molarratio of epoxy:thiol of about 92.5%.

TABLE 1 Resin 1: Component # Component Amount (g) 1 Araldite MY 721 3.242 Tactix 556 1.08 3 TMC 3.13 4 Crystalline Silica (51 wt %) 8.08 5 HMDZFumed Silica (2 wt %) 0.32 6 DMTA 0.15

Araldite MY 721 is a polyepoxy of the formula:

Tactix 556 is a polyepoxy of the formula:

TMC is a polythiol of the formula:

DMTA is a tertiary amine of the formula:

Resin 1 was prepared by mixing the appropriate amount of components 1-5shown in Table 1. These components were mixed for 1 minute at 2300 rpmin a centrifugal mixer (DAC 600.1 FVZ, Flacktek) followed by handmixing. The mixture was allowed to cool in room temperature water for 30minutes before adding component 6 and mixing at 2300 rpm for anadditional 15 seconds. This mixed resin sample was cured at 75° F.±5° F.for 14 days and was tested for compressive strength according to ASTM695. For elevated temperature testing, samples and compression platenswere held at 88° C. (190° F.) for ten minutes longer than it took forthe platens to thermally equilibrate within the thermal chamber.

In some examples, a difference in the molar ratio of polythiol topolyepoxy compounds of the starting compositions of a first resin and asecond resin results in different compressive strengths of the tworesins. A ratio of polythiol to polyepoxy compounds of the startingcomposition of a resin may deviate from the typical 1:1 molar ratio.Without being bound by theory, a subtle change in the molar ratio mayaffect reactivity and resin network formation. Compressive strengthdeviation of two or more resins by adjusting the ratio of polythiol topolyepoxy compounds may be monitored by the glass transition temperatureof a cured resin.

For example, the stoichiometric composition in epoxy-thiol Resin 1 wasmonitored through Dynamic Mechanical Analysis (DMA, TA Q800). For agiven amount of thiol, the molar ratio based on epoxy to thiol compoundwas screened in 5% increments where it was found that the glasstransition (Tg) for resin 1 upon heating at 3° C./min was optimized atabout 90% epoxy to thiol compounds (line 102), as shown in FIG. 1. Asshown in FIG. 1, storage modulus (MegaPascals (MPa)) as a function oftemperature for Resin 1 was lowest across a wide range of temperatures(room temperature to 221° F.) where the ratio of polyepoxy to polythiolcompounds was 1:1 (i.e., 100% epoxy) (line 104). As described herein,“room temperature” is defined as a temperature between about 65° F. toabout 80° F., such as about 70° F. Storage modulus at a giventemperature of 85% epoxy (line 106) and 95% epoxy (line 108) is eachlower than 90% epoxy (line 102).

Using the 90% epoxy/thiol ratio (line 102) of Resin 1, compressivestrength samples were prepared and aged for two weeks at roomtemperature before testing. As shown in FIG. 2, Resin 1 (90%epoxy/thiol) (line 202) has a compressive strength of 17.2 ksi at roomtemperature. These results indicate how Resin 1 (90% epoxy/thiol) iscomparable in compressive strength at 2% offset compared to the EA9377epoxy-amine benchmark resin (line 204).

For compressive strength at elevated temperatures, a compressivestrength sample of the 90% epoxy/thiol ratio of Resin 1 was prepared andaged for two weeks at room temperature, followed by placing the samplein a thermal chamber for compressive strength testing. The chamber wasleft to equilibrate at 190° F. and then a 10 min soak was applied afterequilibration before initiating the compression testing. As shown inFIG. 3, Resin 1 (90% epoxy) (line 302) has a compressive strength of 9.8ksi and 432 ksi modulus at 190° F. Resin 1 (90% epoxy) indeedoutperforms epoxy-amine EA9377 (line 304), indicating the benefit oftighter crosslinking density in the epoxy-thiol system which improvescompressive strength performance.

Given the higher compressive strength performance at 190° F. of Resin 1(90% epoxy), additional testing was performed at 221° F. (105° C.) wherediffering soak times were compared. For the resins of FIG. 3,compressive strength testing utilized a method of bringing the thermalchamber and sample up to temperature (190° F.) and then holding forapproximately 10 mins following equilibration. The potential for higherperformance due to a higher degree of curing or network crosslinking wasinvestigated by extending the soak time to approximately 240 mins beforecompressing. As shown in FIG. 4, an increase in compressive strength isobserved for Resin 1 (90% epoxy) with soak time to approximately 240mins (line 402) as compared to Resin 1 (90% epoxy) that was heated to190° F. and held at approximately 10 mins following equilibration (line404).

EXAMPLE 2: RESIN 2: POT LIFE AND CURE TIME

Following the general procedure for preparation of Resin 1, Resin 2 wasprepared with the same composition as Resin 1, except 2% (w/w) of a saltform of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was used instead ofneutral DMTA. Both salt forms and neutral forms of tertiary amines, suchas DBU and DMTA, impart latent cure properties to pre-cured epoxy-thiolresins, which allows longer working life at room temperature but fasterkinetics at elevated temps (140° F.). In order to determine workablepot-life of Resin 2, the shear modulus (G′) was monitored at 25° C. Asshown in FIG. 5, Resin 2 (line 502) experiences minimal thickening up toabout 100 minutes, demonstrating an acceptable working life, as comparedto epoxy-amine EA9377 resin (line 504).

Demonstration of cure kinetics with elevated temperature curing at 140°F. of Resin 2 was also evaluated by measuring shear modulus (G′) versustime and comparing the modulus rise of epoxy-amine EA9377. As shown inFIG. 6, Resin 2 (line 602) was able to achieve a modulus plateau wellwithin 30 minutes at 140° F. while epoxy-amine EA9377 resin (line 604)reached its plateau in 60 minutes at 140° F. or beyond. Therefore, Resin2 may be cured at about 140° F. to acceptable hardness within about30-minutes, unlike an epoxy-amine EA9377 resin.

In some examples, a slower cure may be favored to increase work time ofa liquid shim. As shown in FIG. 7, Resin 1 (90% epoxy-thiol) (line 702)gives an accelerated cure of less than 20 mins at 140° F. Nonetheless,an ambient cure (room temperature) of Resin 1 (line 702) has a pot lifeof about 90 min in addition to a sharp cure transition to the same shearmodulus as that observed for the accelerated cure. An increased curetime/pot life may also be achieved by cooling the composition ofpre-cured Resin 1. In some examples, pre-cured Resin 1 may be cooled tobetween about −200° F. to about 32° F., such as about −100° F. to about−50° F. Cooling pre-cured Resin 1 allows for transportation of thecomposition before application as a resin. Alternatively, pre-curedepoxy-thiol composition may be transported without an amine catalyst,and the amine catalyst may be introduced to the composition to initiatecuring. For example, a composition of components 1 through 5 of Resin 1may be transported. Just before resin formation, component 6 (e.g., atertiary amine) is added to the composition to initiate curing andformation of Resin 1.

EXAMPLE 3: RESIN 3

Following the general procedure for preparation of Resin 1, Resin 3 wasprepared with the same composition (as shown in Table 2) as Resin 1,except Tactix 556 was not used and the amount of TMC was increased togive a 1:0.925 molar ratio of Araldite MY 721 to TMC.

TABLE 2 Resin 3: Component # Component Amount (g) 1 Araldite MY 721 3.002 TMC 2.47 3 Crystalline Silica (1-10 μm powder) 6.19 4 HMDZ FumedSilica 0.24 5 DMTA 0.24

Resin 3 and epoxy-amine EA9377 resin were each formed by a cure at 140°F. for 240 mins. As shown in FIG. 8a , Resin 3 (line 802) has acompressive stress of about 8.7 ksi at 2% offset at 190° F. Resin 3,therefore, has a higher compressive stress than epoxy-amine EA9377 resin(line 804) at 190° F.

As shown in FIG. 8b , Resin 3 (line 806) has a compressive stress ofabout 16.3 ksi at 2% offset at room temperature. Resin 3, therefore, hasa comparable compressive stress as epoxy-amine EA9377 resin (line 808)at room temperature.

Comparative Example: Resin 1 vs. Resin 4

The composition of Resin 1 is as described for Example 1 in Table 1(above). Following the general procedure for preparation of Resin 1,Resin 4 (as shown in Table 3) was prepared with the same composition asResin 1, except Epon 828 was used instead of both Araldite MY 721 andTactix 556, and DMP-30 was used instead of DMTA.

TABLE 3 Resin 4: Component # Component Amount (g) 1 Epon 828 3.24 2 TMC1.08 3 Micro Silica (51 wt %) 8.08 4 HMDZ Fumed Silica (2 wt %) 0.32 5DMP-30 0.1

Epon 828 is a polyepoxy compound of the formula:

DMP-30 is a tertiary amine of the formula:

As shown in FIG. 9, Resin 1 has higher compressive strength than Resin 4at both room temperature compression (line 902) and 190° F. compression(line 904). Compressive strength of Resin 4 at room temperaturecompression is shown at line 906. Resin 4 does not demonstrate anyreasonable compressive strength performance at elevated temperature(190° F.) as shown at line 908.

Epoxy-thiol resins described herein may be pre-mixed and prepared on avehicle component for use as a film-adhesive, for example, in caseswhere gaps are narrower than about 3 millimeters. Vehicle componentsinclude aircraft components, automobile components, marine components,and the like. After the filming process, the epoxy-thiol material may befrozen to arrest cure progression until the time of installation.Pre-mixed epoxy-thiol resins may be applied onto coated or uncoatedaircraft components such as panels, coated lap joints between two ormore panels, wing-to-fuselage assemblies, and structural aircraftcomposite or metallic part; e.g., fuselage body-joint or wingrib-to-skin joint. The pre-mixed epoxy-thiol resins are typicallyprepared by mixing a polyepoxy compound, a polythiol compound, a fillermaterial, and a tertiary amine and thereafter applying the resultantcomposition(s) onto a vehicle component. The term, “applying” includesany deposition method (for example, dipping, coating, spraying, etc.).The pre-cured epoxy-thiol resins disclosed herein possess favorablereaction kinetics for preparing sheets having one or more cured resinlayers with compressive strength of at least 14 ksi at 2% offset roomtemperature and at least 8 ksi at 2% offset at 190° F.

Epoxy-thiol resins described herein may also be used as a component ofprepreg materials, for example, in cases where gaps are wider than about3 millimeters. For example, epoxy-thiol resins described herein may beimpregnated into fiber materials composed of graphite, fiberglass,nylon, Kevlar® and related materials (for example, other aramidpolymers), spectra, among others.

Epoxy-thiol resins described herein have compressive strength equivalentto or exceeding current state of the art epoxy-amine resins. Withoutbeing bound by theory, compressive strength of epoxy-thiol resinsdescribed herein are likely due to, for example, (1) low averagedistance between reactive thiol moieties in the polythiol precursorwhich increases crosslinking density, and (2) how the ratio of epoxy tothiol reactive groups affects compressive strength.

Pre-cured epoxy-thiol resins described herein have a thiol to epoxyratio that produces resins with high compressive strengths at both roomtemperature and elevated temperature (for example, from about 190° F. toabout 221° F.). Epoxy-thiol resins described herein have a compressivestrength of about 14 ksi or greater at 2% offset at room temperature.Epoxy-thiol resins described herein have a compressive strength of about8 ksi or greater at 2% offset at 190° F. Pre-cured epoxy-thiol resinsdescribed herein are rapidly cured at elevated temperature (e.g., 15mins or less at 140° F.), have a pot life of about 90 minutes or more,and have room temperature cure of about 2.5 hours or less. Pre-curedepoxy-thiol resins described herein allow for a composition that isdormant in the uncatalyzed state (e.g., in the absence of a tertiaryamine) but capable of being catalyzed to accelerate curing. In addition,the mechanical properties of epoxy-thiol resins described herein havecompressive strength that meets or exceeds that of the current state ofthe art epoxy-amine liquid shims. Epoxy-thiol resins described hereinare superior to epoxy-amine resins for thin film applications such asmoldable plastic shims because the pre-cured epoxy-thiol resins are lesssusceptible to reactions with atmospheric moisture and carbon dioxide.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the present disclosure may be devisedwithout departing from the basic scope thereof. Furthermore, while theforegoing is directed to epoxy-thiol resins as applied to the aerospaceindustry, aspects of the present disclosure may be directed to otherapplications not associated with an aircraft, such as applications inthe automotive, marine, energy industry, and the like.

What is claimed is:
 1. A resin that is the reaction product of: one ormore polythiols having between two and about ten thiol moieties; one ormore polyepoxides having between two and about ten epoxy moieties at amolar ratio of polyepoxides to polythiols of about 0.9; and one or moreamine catalysts of the formula NR₁R₂R₃, wherein each of R₁, R₂, and R₃is independently linear or branched C1-20 alkyl or two or more of R₁,R₂, and R₃ combine to form cycloalkyl.
 2. The resin of claim 1, whereinthe resin has a compressive strength of at least 14 ksi at 2% offset at70° F. and at least 8 ksi at 2% offset at 190° F.
 3. The resin of claim1, further comprising one or more solid particulate fillers.
 4. Theresin of claim 3, wherein the one or more solid particulate fillers isbetween about 50% wt to about 55% wt of the resin.
 5. The resin of claim1, wherein at least one of the one or more polythiols is of the formulaSH—R—SH, wherein R is selected from the group consisting of alkyl,cycloalkyl, thiol-substituted alkyl, and thiol-substituted cycloalkyl.6. The resin of claim 1, wherein each instance of the polythiol isindependently selected from the group consisting of1,2,3-propanetrithiol, 1,2,4-tris(2-mercaptoethyl) cyclohexane, and1,3,5-tris(2-mercaptoethyl) cyclohexane.
 7. The resin of claim 1,wherein each instance of the solid particulate fillers is independentlyselected from the group consisting of crystalline silica, fumed silica,methylated fumed silica, alumina, mica, silicate, talc, aluminosilicate,barium sulfate, diatomite, calcium carbonate, calcium sulfate, carbon,and wollastonite.
 8. The resin of claim 1, wherein each instance of theone or more amine catalysts is independently selected from the groupconsisting of diisopropylethylamine, N-alkyl-piperidine,N-alkyl-piperazine, 1,4-diazabicyclo[2.2.2]octane,1,8-diazabicyclo[5.4.0]undec-7-ene, trimethylamine, triethylamine,tripropylamine, N,N-dimethylethylamine, N,N-dimethylpropylamine,N,N-dimethylbutylamine, N,N-dimethylpentylamine, N,N-dimethylhexylamine,N,N-dimethylheptylamine, N,N-dimethyloctylamine, N,N-dimethylnonylamine,N,N-dimethyldecylamine, N,N-dimethylundecylamine,N,N-dimethyldodecylamine, N,N-dimethyltridecylamine,N,N-dimethyltetradecylamine, N,N-dimethylpentadecylamine, N,N-dimethylhexadecylamine, N,N-dimethylheptadecylamine,N,N-dimethyloctadecylamine, N,N-dimethylnonadecylamine,N,N-dimethyleicosylamine, N,N-diethylpropylamine, N,N-diethylbutylamine,N,N-diethylpentylamine, N,N-diethylhexylamine, N,N-diethylheptylamine,N,N-diethyloctylamine, N,N-diethylnonylamine, N,N-diethyldecylamine,N,N-diethylundecylamine, N,N-diethyldodecylamine,N,N-diethyltridecylamine, N,N-diethyltetradecylamine,N,N-diethylpentadecylamine, N,N-diethylhexadecylamine,N,N-diethylheptadecylamine, N,N-diethyloctadecylamine, N,N-diethylnonadecylamine, N,N-diethyleicosylamine,N,N-dipropylbutylamine, N,N-dipropylpentylamine, N,N-dipropylhexylamine,N,N-dipropylheptylamine, N,N-dipropyloctylamine, N,N-dipropylnonylamine,N,N-dipropyldecylamine, N,N-dipropylundecylamine,N,N-dipropyldodecylamine, N,N-dipropyltridecylamine,N,N-dipropyltetradecylamine, N,N-dipropylpentadecylamine,N,N-dipropylhexadecylamine, N,N-dipropylheptadecylamine,N,N-dipropyloctadecylamine, N,N-dipropylnonadecylamine, andN,N-dipropyleicosylamine.
 9. The resin of claim 8, wherein the one ormore amine catalysts is N,N-dimethyltetradecylamine.
 10. The resin ofclaim 1, wherein the one or more amine catalysts is a salt.
 11. Theresin of claim 1, wherein the one or more amine catalysts is betweenabout 0.1% wt to about 10% wt of the resin.
 12. The resin of claim 1,wherein the one or more amine catalysts is between about 1% wt to about3% wt of the resin.
 13. The resin of claim 1, wherein at least one ofthe one or more polyepoxides has between four and about ten epoxymoieties.
 14. The resin of claim 1, wherein each instance of the one ormore polyepoxides is independently selected from the group consisting ofN,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane, poly[(phenylglycidyl ether)-codicyclopentadiene], tetraphenylolethane glycidylether, and tris(4-hydroxyphenyl)methane triglycidyl ether.
 15. The resinof claim 14, wherein at least one of the one or more polyepoxides istetraphenylolethane glycidyl ether or tris(4-hydroxyphenyl)methanetriglycidyl ether.
 16. The resin of claim 14, wherein the one or moreamine catalysts is N,N-dimethyltetradecylamine.
 17. A resin that is thereaction product of: a polythiol having an equivalent molecular weightof between about 20 to about 115; and a polyepoxide having between fourand about ten epoxy moieties; a solid particulate filler; wherein theresin has a compressive strength of at least 14 ksi at 2% offset at 70°F. and at least 8 ksi at 2% offset at 190° F.
 18. The resin of claim 17,wherein the molar ratio of polyepoxide to polythiol is about 0.9. 19.The resin of claim 17, wherein the polythiol is1,2,4-tris(2-mercaptoethyl)cyclohexane and the polyepoxide is of theformula:


20. A composition comprising: one or more polythiols having between twoand about ten thiol moieties; and one or more polyepoxides havingbetween two and about ten epoxy moieties at a molar ratio ofpolyepoxides to polythiols of about 0.9.
 21. The composition of claim20, further comprising a solid particulate filler.
 22. The compositionof claim 21, further comprising an amine catalyst.